Listen for changes with localStorage on the same window

Question

I want to listen for changes that are happening in the localStorage API on the same page (Not in multiple tabs like the spec says).

I am currently using this code:

var storageHandler = function () {
    alert('storage event 1');
  };

  window.addEventListener("storage", storageHandler, false);

localStorage.setItem('foo', 'bar');

Does anyone know a vanilla JavaScript way to listen to events on localStorage on one page (no jQuery)

Answer 1

Since JS is dynamical language just rewrite original functions.

var originalSetItem = localStorage.setItem; 
localStorage.setItem = function(){
    document.createEvent('Event').initEvent('itemInserted', true, true);
    originalSetItem.apply(this, arguments);
}

Answer 2

Updated above answer, as document.createEvent now is part of an old, deprecated API.

const originalSetItem = localStorage.setItem;

localStorage.setItem = function(key, value) {
  const event = new Event('itemInserted');

  event.value = value; // Optional..
  event.key = key; // Optional..

  document.dispatchEvent(event);

  originalSetItem.apply(this, arguments);
};

const localStorageSetHandler = function(e) {
  alert('localStorage.set("' + e.key + '", "' + e.value + '") was called');
};

document.addEventListener("itemInserted", localStorageSetHandler, false);

localStorage.setItem('foo', 'bar'); // Pops an alert

https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Creating_and_triggering_events